There are known the following compositions used for making an air-bag cover:
(1) an olefin-based thermoplastic elastomer composition containing (a) 20 to 60 parts by weight of a propylene-ethylene random copolymer having a melt flow rate of 10 to 120 g/10 minutes measured at 230° C. under a load of 2.16 kg, and containing an ethylene unit in an amount of 2.0 to 4.5% by weight, (b) 5 to 40 parts by weight of a low-density polyethylene, and (c) 60 to 20 parts by weight of an ethylene-based copolymer rubber having a Mooney viscosity (ML1+4, 100° C.) of 50 to 120 (JP 8-27331A);
(2) a thermoplastic elastomer composition having a flexural modulus of 100 to 600 MPa and a coefficient of linear expansion of 9×10−5 cm/cm/° C. or smaller, which comprises (A) 30 to 70% by weight of a propylene-based copolymer resin, and (B) 70 to 30% by weight of a copolymer rubber of ethylene with an α-olefin having 4 or more carbon atoms (JP 10-265628A);
(3) an olefin-based thermoplastic elastomer comprising (A) a propylene-based resin and (B) an olefin-based copolymer rubber, and having a ratio (N1/SS) of first normal stress difference (N1) to shear stress (SS) of 0.6:1 to 1.4:1 said first normal stress difference (N1) and shear stress (SS) being determined by subjecting said elastomer to step shear test at a temperature of 200° C. and a shear rate of 25.1 sec−1 (U.S. Pat. No. 6,476,139B2 corresponding to JP 2001-279030A).
The term “air-bag cover” in the present invention means a cover used for holding an air-bag, especially a life-saving automotive air-bag.